U.S. patent number 7,226,669 [Application Number 10/926,287] was granted by the patent office on 2007-06-05 for high strength aluminium alloy brazing sheet, brazed assembly and method for producing same.
This patent grant is currently assigned to Aleris Aluminum Koblenz GmbH. Invention is credited to Rinze Benedictus, Achim Burger, Alfred Johann Peter Haszler.
United States Patent |
7,226,669 |
Benedictus , et al. |
June 5, 2007 |
High strength aluminium alloy brazing sheet, brazed assembly and
method for producing same
Abstract
The present invention a high strength aluminium alloy brazing
sheet, comprising an Al--Zn core layer and at least one clad layer,
the core layer including the following composition (in weight
percent): TABLE-US-00001 Zn 1.2 to 5.5 Mg 0.8 to 3.0 Mn 0.1 to 1.0
Cu <0.2 Si <0.35 Fe <0.5 optionally one or more of:
TABLE-US-00002 Zr <0.3 Cr <0.3 V <0.3 Ti <0.2 Hf
<0.3 Sc <0.5, the balance aluminium and incidental elements
and impurities. The clad layer includes an Al--Si based filler
alloy and is applied on at least one side of the core layer. The
invention relates furthermore to a brazed assembly including such
brazing sheet, to the use of such brazing sheet and to method for
producing an aluminium alloy brazing sheet.
Inventors: |
Benedictus; Rinze (Delft,
NL), Burger; Achim (Hoeher-Grenzhausen,
DE), Haszler; Alfred Johann Peter (Vallendar,
DE) |
Assignee: |
Aleris Aluminum Koblenz GmbH
(Koblenz, DE)
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Family
ID: |
34426562 |
Appl.
No.: |
10/926,287 |
Filed: |
August 26, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050079376 A1 |
Apr 14, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60499008 |
Sep 2, 2003 |
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Foreign Application Priority Data
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Aug 29, 2003 [EP] |
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03077724 |
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Current U.S.
Class: |
428/654;
228/262.51; 228/235.3; 165/905; 148/535; 148/523 |
Current CPC
Class: |
B23K
1/0012 (20130101); B23K 35/0238 (20130101); B23K
35/288 (20130101); C22C 21/10 (20130101); F28F
21/089 (20130101); B23K 35/002 (20130101); B23K
2103/10 (20180801); Y10T 428/12806 (20150115); Y10T
428/12764 (20150115); B23K 2101/14 (20180801); Y10S
165/905 (20130101) |
Current International
Class: |
B32B
15/20 (20060101); B23K 20/04 (20060101); B23K
35/00 (20060101); C22C 21/00 (20060101); C22F
1/053 (20060101) |
Field of
Search: |
;428/654 ;148/535
;164/91 ;29/469,527.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0587274 |
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Mar 1994 |
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EP |
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0799667 |
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0823305 |
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Feb 1998 |
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EP |
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0829552 |
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Mar 1998 |
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EP |
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1175954 |
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Jan 2002 |
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EP |
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2114601 |
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Aug 1983 |
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GB |
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55161044 |
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59-143040 |
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JP |
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62-287053 |
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JP |
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63-162833 |
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Jul 1988 |
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JP |
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64-047829 |
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Feb 1989 |
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JP |
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02-037991 |
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Feb 1990 |
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JP |
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02-037992 |
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Feb 1990 |
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JP |
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05125477 |
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May 1993 |
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JP |
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05-331580 |
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Dec 1993 |
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JP |
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08-260087 |
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Oct 1996 |
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JP |
|
09176767 |
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Jul 1997 |
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JP |
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63-227753 |
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Sep 1998 |
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JP |
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Other References
H Engstrom et al., Brazing. 18.sup.th International conference.
Abstracts., "Multilayer Clad Aluminum Material With Improved
Brazing Properties", pp. 242-243, vol. 68, 1987. cited by
other.
|
Primary Examiner: Zimmerman; John J.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This claims priority under 35 USC Section 119 from European patent
application serial number 03077724.7 filed with the EPO on Aug. 29,
2003 and U.S. Provisional Patent Application No. 60/499,008 filed
on Sep. 2, 2003, both of which are incorporated herein by reference
in their entirety.
Claims
The invention claimed is:
1. High strength aluminium-zinc alloy brazing sheet, comprising an
Al--Zn core layer, one interlayer on each side of the core layer
and a clad layer on each interlayer, said core layer comprising the
following composition (in weight percent): TABLE-US-00013 Zn 3.0 to
5.0 Mg 1.2 to 2.5 Mn 0.1 to 1.0 Cu <0.2 Si <0.35 Fe
<0.5,
optionally one or more of: TABLE-US-00014 Zr <0.3 Cr <0.3 V
<0.3 Ti <0.2 Hf <0.3 Sc <0.5,
the balance aluminium and incidental elements and impurities, said
clad layer comprising an Al--Si based filler alloy and being
applied on at least one side of the core layer, wherein at least
one of said interlayers comprises either a sacrificial anode
material which is less corrosion resistant than the core layer or a
protective material which is more corrosion resistant than the core
layer, said sacrificial anode material or protective material
comprising Zn, in addition to or instead of Mn, in a range of (in
weight %) 1.0 to 2.5.
2. Brazing sheet according to claim 1, wherein the amount (in
weight %) of Mn in the core layer is in a range of 0.4 to 0.8.
3. Brazing sheet according to claim 1, wherein the amount (in
weight %) of Zr in the core layer is in a range of 0.04 to 0.2.
4. Brazing sheet according to claim 1, wherein said interlayer
comprising said sacrificial anode material or protective material
further comprises either an Al--Mn alloy composition of the
AA3xxx-type or pure aluminium of the AA1 xxx-type or an AlMgSi
alloy of the AA6xxx-type, each optionally with the addition of up
to 3% Zn.
5. Brazing sheet according to claim 4, wherein said interlayer
comprising said sacrificial anode material or protective material
comprises an AlMgSi alloy of the AA6xxx-type, optionally with the
addition Zn.
6. Brazing sheet according to claim 1, wherein said interlayer
comprising said sacrificial anode material or protective material
further comprises an Al--Mn alloy composition comprising the
following composition (in wt. %): TABLE-US-00015 Mn 0.8 1.5 Si
.ltoreq.0.5 Cu .ltoreq.0.5 Mg .ltoreq.0.3 Fe .ltoreq.0.5 Ti
.ltoreq.0.2,
the balance aluminium and incidental elements and impurities.
7. Brazing sheet according to claim 6, wherein said composition of
said interlayer comprises 0.5 2.5% Zn.
8. Brazing sheet according to claim 6, wherein said composition of
said interlayer comprises 1.0 1.5% Zn.
9. Brazing sheet according to claim 1, wherein said clad layer is
applied on both sides of the core layer, wherein at least one of
said interlayers is applied on at least one side of the core layer
between the core layer and the clad layer.
10. Brazing sheet according to claim 1, wherein the amount (in
weight %) of Zn in the core layer is in a range of 3.5 to 5.0.
11. Brazed assembly comprising a brazing sheet according to claim
1, wherein said assembly is composed of four or five layered
brazing sheet, comprising a core layer, an interlayer on each side
of the core layer and a clad layer on at least one interlayer.
12. Brazed assembly according to claim 11, wherein multiple brazing
sheets are superposing each other so that the interlayer which is
alternatively not covered by a clad layer is facing outwardly, and
the superposed brazed sheets are joined together by brazing facing
clad layers.
13. A method of using a brazing sheet according to claim 1,
comprising forming the brazing sheet into a brazing sheet product
or brazing the sheet to be part of a brazed assembly wherein said
assembly is composed of four or five layered brazing sheet,
comprising a core layer, an interlayer on each side of the core
layer and a clad layer on at least one interlayer.
14. High strength aluminium-zinc alloy brazing sheet according to
claim 1, comprising said Al--Zn core layer and said at least one
clad layer, said core layer consisting essentially of the following
composition (in wt. %): TABLE-US-00016 Zn 3.0 to 5.0 Mg 1.2 to 2.5
Mn 0.1 to 1.0 Cu .ltoreq.0.2 Si .ltoreq.0.35 Fe .ltoreq.0.5
optionally one or more of: TABLE-US-00017 Zr <0.3 Cr <0.3 V
<0.3 Ti <0.2 Hf <0.3 Sc <0.5,
the balance aluminium and incidental elements and impurities, said
clad layer comprising an Al--Si based filler alloy and being
applied on at least one side of the core layer.
15. Brazing sheet according to claim 1, wherein said interlayer
comprising said sacrificial anode material or protective material
further comprises an Al--Mn alloy composition consisting
essentially of the following composition (in wt. %): TABLE-US-00018
Mn 0.8 1.5 Si .ltoreq.0.5 Cu .ltoreq.0.5 Mg .ltoreq.0.3 Fe
.ltoreq.0.5 Ti .ltoreq.0.2,
the balance aluminium and incidental elements and impurities.
16. Brazing sheet according to claim 1, wherein said core layer
comprises at most 4.1% Zn.
17. Brazing sheet according to claim 1, wherein said core layer
comprises at least 1.64% Mg.
18. Brazing sheet according to claim 1, wherein said core layer
comprises at least 0.51% Mn.
19. Brazing sheet according to claim 1, wherein said core layer
comprises 0.12 to 0.30% Fe.
20. Brazing sheet according to claim 1, further comprising about
0.03% Ti.
21. Brazing sheet according to claim 1, wherein the ratio of Zn to
Mg (by weight) in the composition is at least 1.8 and at most
3.3.
22. A method for producing an aluminium alloy brazing sheet having
high strength and good corrosion resistance, comprising the steps
of: a) casting a core ingot with the following composition (in
weight percent): TABLE-US-00019 Zn 1.2 to 5.5 Mg 0.8 to 3.0 Mn 0.1
to 1.0 Cu <0.2 Si <0.35 Fe <0.5
optionally one or more of: TABLE-US-00020 Zr <0.3 Cr <0.3 V
<0.3 Ti <0.2 Hf <0.3 Sc <0.5,
the balance aluminium and incidental elements and impurities as a
core material, b) homogenising and/or pre-heating the core ingot
after casting, c) casting a clad ingot comprising an Al--Si based
filler alloy, homogenising and/or pre-heating the clad ingot after
casting and hot rolling said clad ingot into rolled clad member
members, d) superposing said core ingot between said hot rolled
clad members to form a three-layered member, e) hot rolling said
layered member and optionally cold rolling said layered member into
a rolled product, f) optionally inter-annealing said layered member
between cold rolling passes, g) optionally end annealing, and h)
ageing the rolled and optionally inter- and/or end-annealed
product.
23. Method as claimed in claim 22, further comprising casting an
interlayer ingot comprising either an Al--Mn alloy composition of
the AA3xxx-type or pure aluminium of the AA1 xxx-type or an AlMgSi
alloy of the AA6xxx-type, optionally with the addition of Zn up to
3 wt. %, homogenising and/or pre-heating the interlayer ingot after
casting and hot rolling said interlayer ingot to a rolled
interlayer member, and superposing said core ingot, said interlayer
member and said hot rolled clad member to form said layered
member.
24. Method as claimed in claim 22, wherein, a) casting a multiclad
ingot, using a composition of the AA3xxx-type or pure addition of
Zn up to 3 wt. %, as a center core layer and an Al--Mn alloy
composition of the M3xxx-type or pure aluminium of the AA1 xxx-type
or an AlMgSi alloy of the AA6xxx-type, optionally with the addition
of Zn up to 3 wt. %, as an interlayer on both sides of the center
core layer, forms said multiclad ingot, and comprising b) said
homogenising and/or pre-heating said multiclad ingot after casting,
c) said casting a clad ingot comprising an Al--Si based filler
alloy, homogenising and/or pre-heating the clad ingot after casting
and hot rolling said clad ingot to a rolled clad member, and d)
said superposing said multiclad ingot and said hot rolled clad
member to form said layered member.
25. Method according to claim 22, wherein the amount (in weight %)
of Zn in the core layer is in a range of 3.0 to 5.0 and the amount
(in weight %) of Mg in the core layer is in a range of 1 .2 to
2.5.
26. Method according to claim 22, wherein the amount (in weight %)
of Mn in the core layer is in a range of 0.4 to 0.8.
27. Method according to claim 22, wherein the amount (in weight %)
of Zr in the core layer is in a range of 0.04 to 0.2.
28. Method according to claim 22, wherein the amount (in weight %)
of Zn in the core layer is in a range of 3.5 to 5.0.
29. Method as claimed in claim 22, comprising end-annealing the
rolled product.
Description
FIELD OF THE INVENTION
The present invention relates to an aluminium alloy brazing sheet
for brazing which has high strength and improved brazing
properties, to a brazed assembly comprising such brazing sheet, to
the use of such brazing sheet and to a method for producing an
aluminium alloy brazing sheet. More specifically, the present
invention relates to a high strength multi-layer clad aluminium
alloy material with improved brazing properties, comprising an
interlayer between cladding and core, thereby improving corrosion
resistance and reducing penetration of silicon and magnesium during
brazing. The present invention also relates to a method for roll
cladding or cast cladding the multi-layer clad brazing sheet.
DESCRIPTION OF THE RELATED ART
It is known in the art to use aluminium alloy brazing sheet for
use, for example, in heat exchangers, oil coolers, inter coolers,
evaporators or condensers of automobiles or other vehicles or
applications using heat exchangers. Conventionally, these
assemblies are manufactured from brazing sheets for brazing, using
Al--Mn based aluminium alloys or Al--Mg--Si based aluminium alloys
as a core material and Al--Si based aluminium alloys, typically of
the AA4xxx-series alloys, as a clad brazing filler material for
conventional brazing applications. Once these brazing sheets are
assembled to e.g., a heat exchanger for automobiles, a cooling
medium or a heating medium is charged through the assembly. Hence,
it is crucial to prevent leakage of the assembly such as a heat
exchanger while at the same time reducing the weight and size of
such assemblies. Therefore, recent developments showed assemblies
made from brazing sheets which were improved to reduce the size,
weight and cost by decreasing the material thickness and changing
the structure of the heat exchanger.
To improve the brazing quality and durability properties of the
heat-treatable alloys of the brazing sheet a multi-layer clad
aluminium material was developed, see H. Engstrom and L.-O.
Gullman, "A Multilayer Clad Aluminium Material with Improved
Brazing Properties", 18.sup.th International AWS Brazing
Conference, of Mar. 24 26, 1987 in Chicago. In this paper it is
proposed to use an interlayer between the braze cladding and the
core layer in order to increase the corrosion resistance.
Furthermore, the results showed that silicon penetration along
grain boundaries of the core layer was significantly delayed in
such multilayered material compared to standard
"core-braze"-material and more silicon remained in the clad layer
and the penetration depth was reduced.
JP-09176767 discloses an aluminium brazing sheet for vacuum brazing
comprising a core layer with the following composition (in weight
%): Cu 0.10 to 0.80, Mn 0.30 to 1.5, Ti 0.01 to 0.20, the balance
aluminium with inevitable impurities, a brazing filler layer having
a composition consisting of (in weight %): Si 5.0 to 15, Mg 0.30 to
2.5, the balance aluminium with inevitable impurities as well as an
intermediate sacrificial corrosion layer composed of a 7xxx-type
aluminium alloy containing at least (in weight %) 2.0 5.0 Zn.
EP-0823305-A2 discloses a brazing sheet with good corrosion
resistance for use in heat exchangers comprising a core layer with
the following composition (in weight %): Cu 0.15 0.35, Mn 0.50 1.6,
Mg 0.05 0.50, Ti 0.06 0.30, the remainder aluminium and unavoidable
impurities, a clad layer comprising an Al--Si--Mg type cladding
material and an intermediate layer with (in weight %) Mn: 0.50 1.2,
the remainder aluminium and unavoidable impurities as well as Mg:
0.05 1.20 as an option, thereby also disclosing the addition of Zn
in an amount of (in weight %) 1.0 5.0. These multi-layered brazing
sheets showed tensile properties after brazing of 140 MPa to 165
MPa.
EP-0799667-A1 discloses an aluminium alloy brazing sheet for brazed
heat exchangers comprising a core layer with the following
composition (in weight %): Zn 0.05 to 1.2 (optionally), Mn 0.50 to
1.5, Si.ltoreq.0.60, Fe.ltoreq.0.70, the balance aluminium and
inevitable impurities, wherein the inevitable impurities are
restricted to 0.60 wt % or below of Si and 0.70 wt % or below of
Fe. Furthermore, such brazing sheet incorporates a clad layer of
the Al--Si based filler alloy type and an intermediate layer
comprising aluminium and inevitable impurities which are limited to
a total amount of 1.0 wt %. The intermediate layer has a pitting
potential which is lower than that of the core layer so that the
intermediate layer can be used as a sacrificial layer to deflect
the corrosion path.
EP-1175954-A1 discloses a multi-layer aluminium alloy brazing sheet
with a core layer comprising the following composition (in wt. %):
Cu 0.20 to 1.0, Mn 0.30 to 1.5, Mg.ltoreq.0.30, Si 0.30 to 1.3,
Fe.ltoreq.0.20, the balance aluminium and inevitable impurities, a
brazing filler material being formed on one surface of the core
material comprising an Al--Si based aluminium alloy and a cladding
material which is formed on the other side of the core material and
which contains (in wt. %): Mg 2.0 to 3.5, Zn 0.50 to 2.0,
Si.ltoreq.0.20, the balance aluminium and inevitable
impurities.
Furthermore, it is disclosed that it is not preferred to add Mg to
the core material, even though the adding of Mg improves the
strength of the brazing sheet, since in a NOCOLOK (registered trade
mark) flux brazing method, the brazing property of a brazing sheet
in which magnesium is added to a core material is significantly
degraded. During brazing the magnesium penetrates to the surface of
the clad brazing layer and effects the NOCOLOK flux salt and the
flux salt ameliorates the brazing properties within the
furnace.
US-2002/0037426-A1 discloses an aluminium alloy brazing sheet for a
heat exchanger having a four-layered structure with a core
material, a clad layer with a filler alloy of an Al--Si alloy and a
sacrificial anode material for an intermediate layer (interlayer)
of an Al--Zn alloy wherein the core alloy is composed of (in wt.
%): Cu 0.05 0.50, Mn 0.05 2.0, Fe 0.20 0.80, Si 0.10 0.50, the
balance aluminium and unavoidable impurities, and wherein the
intermediate layer is composed of a composition comprising (in wt.
%): Cu 0.40 1.0, Mn 0.50 2.0, Si 0.10 0.50, Fe 0.20 0.80, the
balance aluminium and unavoidable impurities.
SUMMARY OF THE INVENTION
Since it has been difficult to obtain a brazing sheet which does
not only have good brazing properties and formability
characteristics but also a high strength and an improved corrosion
resistance it is a preferred object of the present invention to
obtain these. More specifically, it is a preferred object of the
present invention to increase the strength after brazing from about
50 MPa of the conventional AA3xxx-alloy to at least 100 MPa and at
the same time obtaining a high incipient melting point for the core
layer in order to be able to produce light brazing assemblies
having less thickness and less weight.
Finally, it is a preferred object of the present invention to
disclose a method for producing a high strength aluminium alloy
brazing sheet and/or a brazed assembly which manufacturing costs
are lower than those of conventional methods thereby using thinner
materials to accomplish light weight and lower manufacturing cost
as well as simultaneously producing a multiclad or multilayered
aluminium material.
The present invention preferably solves one or more of the
above-mentioned objectives.
A high strength aluminium-zinc alloy brazing sheet according to the
present invention comprises an Al--Zn core layer and at least one
clad layer, the core layer comprising the following composition (in
wt. %):
TABLE-US-00003 Zn 1.2 to 5.5 Mg 0.8 to 3.0 Mn 0.1 to 1.0 Cu <0.2
Si <0.35 Fe <0.5, preferably <0.30
optionally one or more selected from the group consisting of:
TABLE-US-00004 Zr <0.3 Cr <0.3 V <0.3 Ti <0.2 Hf
<0.3 Sc <0.5,
the balance aluminium and incidental elements and impurities, each
<0.05%, total <0.15%, the clad layer comprising an Al--Si
based filler alloy, typically of the AA4xxx-series type having a
Si-content in a range of 5 to 15 wt. %, and being placed on at
least one side of the core layer.
In a further aspect of the invention there is provided a method of
manufacturing such a high strength aluminium brazing sheet
product.
Preferred embodiments are described in the present
specification.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As will be appreciated herein below, except as otherwise indicated,
all percentages are by weight. Furthermore, alloy designations and
temper designations refer to the Aluminum Association designations
in Aluminum Standards and Data and the Registration Records, as
published by the Aluminum Association.
It has been found that the balance of Mg to Zn is of importance.
Depending on the amount of Zn the amount (in wt. %) of Mg is
preferably in between 1.8.ltoreq.[Zn]/[Mg].ltoreq.3.3. Furthermore,
the amount of Zn is reduced compared to regular AA7xxx-type alloys
in order to increase the melting temperature for brazing
applications. By reduction of Cu to amounts of less than 0.2 (in
wt. %) and selecting Zn and Mg in the above identified amounts the
melting temperature of the core layer of the present invention
could be increased up to 620.degree. C. Hence, it has been found
that the amount (in wt. %) of Zn is preferably in a range of 3.0 to
5.0, more preferably in a range of 3.5 to 5.0, even more preferably
in a range of 3.9 to 4.5, and most preferably in between 4.1 to
4.5.
Magnesium, together with Zn, improves the mechanical strength by
aging precipitation of a compound Mg.sub.2Si. However, an excessive
amount of Mg results in penetration of Mg into the clad filler
alloy and a reaction with a brazing salt flux, e.g. NOCOLOK salt.
Magnesium is, however, helpful for enhancing the formability of the
core material. It has been found that an amount (in weight %) of
magnesium in the core layer is preferably having a upper limit of
2.5%, and more preferably is in a range of 1.2 to 2.5, preferably
in a range of 1.3 to 1.95.
Manganese is an element for increasing the corrosion resistance and
the strength of the core material. Since Mn adds to the mechanical
strength without decreasing corrosion resistance, as opposed to Cu,
it has been found that the amount (in wt. %) of Mn in the core
layer is preferably having a lower limit of 0.4. The preferred
upper limit for the Mn content is 0.8, more preferably 0.7, and
most preferably about 0.5, that means about 0.48 to 0.52. However,
too high amounts of Mn result in larger intermetallic compounds
which have a negative effect on processability and corrosion
resistance. Mn also makes the electric potential of the core
material higher thereby assisting in improving the corrosion
resistance.
Silicon and copper contribute to improving the strength of the
alloy by forming a solid solution in the matrix after brazing. An
intermetallic compound composed of Mg.sub.2Si is precipitated by
reaction of Si with Mg from the core layer. However, the Cu content
must be balanced with regard to an optional additional sacrificial
interlayer since the addition of Cu increases the electric
potential of the resultant alloy which becomes more noble. It is
therefore preferred to select the amount (in wt. %) of each of Cu
and/or Si in the core layer in a range of preferably 0.2 or less,
each of these elements preferably in a range of less than 0.1.
Iron enhances the formation of large intermetallic compounds which
distribute throughout the alloy thereby preventing the alloy from
being cracked during forming. However, Fe refines crystal grains
thereby degrading the brazing properties. Hence, the amount (in
weight %) of Fe in the core layer should preferably be in a range
of less than 0.5, preferably less than 0.3, and more preferably in
a range of 0.12 to 0.30.
Zirconium, when added, is in a preferred embodiment in a range of
0.04 to 0.2 (in wt. %), and more preferably in a range of 0.12 to
0.17, and is believed to contribute to the control of the grain
size structure. Too high levels of Zr are to be avoided, since Zr
enhances the formation of intermetallic compounds thereby degrading
processability of the aluminium brazing sheet and the corrosion
resistance. This is equally valid for Ti which should be below 0.15
wt %, preferably about 0.03 wt %. Ti can be added also as a grain
refiner for the cast structure, either as element or as known
titanium boride or titanium carbide grain refiners.
The elements Cr, V, Hf and Sc can be added to assist in controlling
amongst others the grain structure of the product, but they also
have an effect on quench sensitivity during manufacturing of the
core alloy sheet. The optimum levels of these elements depend on
the processing of the core sheet, but on an individual basis the
amount should not exceed the defined ranges. When two or more of
these elements are used, the sum of such combined elements should
preferably not exceed 0.3% (in wt. %), and more preferably it
should not exceed 0.26 wt. %. Too high levels of these elements are
to be avoided, since zirconium enhances the formation of
intermetallic compounds thereby degrading processability of the
aluminium brazing sheet and possibly also the corrosion
resistance.
A preferred embodiment comprises a core layer as described and a
clad layer being formed on both sides of the core layer. Such
brazing sheet may be used in various applications where both sides
are used for the assembly of the brazing sheet.
According to another preferred embodiment an interlayer is formed
on at least one side of the core layer wherein the interlayer
comprises either a sacrificial (anode) material which is less
corrosion resistant than the core layer or a protective material
which is more corrosion resistant than the core layer. Preferably,
the interlayer comprises either an Al--Mn alloy composition of the
AA3xxx-type or pure aluminium of the AA1xxx-type or an AlMgSi alloy
of the AA6xxx-series type, preferably each with the addition of up
to 3 wt. % Zn.
Through the use of an interlayer between the core layer and the
clad layer comprising the filler material, one or more of the
following advantages are obtained:
Firstly, the overall corrosion resistance can be enhanced while--at
the same time--high strength can be achieved and maintained
throughout the use of Zn. Thereby, it is possible to use brazing
sheets with a lower thickness having a lower weight and being less
expensive. With the use of an interlayer the corrosion properties
of the brazing sheet according to the invention are comparable to
conventional AA3xxx-type core materials or AA6xxx-type
materials.
Secondly, a higher melting temperature can be obtained by using two
interlayers one on each side of the core layer. The incipient
melting point of a layered structure comprising a core layer with
an alloy of the present invention and two interlayers as well as a
clad layer on one or both sides of the layered structure diminishes
or reduces the problem of a reduced melting temperature of a core
material which contains more Zn.
Thirdly, the interlayer serves as a barrier layer and prevents the
diffusion of Mg from the core layer to the clad layer and the
diffusion of Si from the clad layer to the core layer. By such
reduction of element migration throughout the layers improved
properties of the brazing sheet are achieved like better
brazeability and mechanical properties.
A preferred interlayer comprises an Al--Mn alloy composition
comprising the following composition (in weight %):
TABLE-US-00005 Mn 0.8 1.5 Si .ltoreq.0.5 Cu .ltoreq.0.5 Mg
.ltoreq.0.3 Fe .ltoreq.0.5 Ti .ltoreq.0.2,
the balance aluminium and incidental elements and impurities, each
<0.05%, total <0.20%.
Even more preferred, the interlayer comprises zinc, in addition to
or instead of manganese, preferably in a range of (in weight %) up
to 3%, preferably in a range of 0.5 to 2.5, most preferably in a
range of 1.0 to 1.5. The addition of zinc makes the electric
potential of the sacrificial anode material less noble than that of
the core alloy in order to ensure the corrosion resistance effect.
The effect of adding zinc is insufficient when the amount is not
enough. However, if zinc is added in a too high amount exceeding
the melting point of the alloy is decreased in the direction of the
brazing temperature.
It has furthermore been found that a reduction of manganese in the
interlayer, thereby being partially replaced by zinc, enhances the
corrosion resistance. The interlayer deflects the corrosion path
thereby protecting the core layer from being effected.
According to another preferred embodiment of the present invention
the interlayer is made of an AA1xxx-type alloy acting as a
protective layer. Here, it is also possible to add zinc for
controlling the electrical potential of such layer compared to the
core layer. In general, it is advantageous to use an interlayer
which is less corrosion resistant, e. g. a sacrificial interlayer
which is considerably invariant to mechanical damage like holes or
scratches.
According to another preferred embodiment of the invention the clad
layer is formed on both sides of the core layer while the
interlayer is formed on at least one side of the core layer in
between the core layer and the clad layer. Since a brazing sheet
has usually one side which is exposed to a corrosive atmosphere
such side should contain the interlayer in between the core layer
and the clad layer in order to protect the core layer from
corrosion after brazing. The ratio of thickness of the core layer
and the interlayer is preferably in a range of 10.ltoreq.core
layer/interlayer.ltoreq.50, wherein the interlayer has preferably a
thickness of at least 40 .mu.m. Such thickness is advantageous for
multiclad or multilayered brazing sheets of about 0.4 to 2.0 mm in
total thickness.
The thickness of the core layer (in percent compared to the total
thickness of the brazing sheet) is preferably in a range of 60 to
90%, the thickness of the interlayer (in percent compared to the
total thickness of the brazing sheet) is preferably in a range of 5
to 25% and the thickness of the clad layer is preferably (in
percent compared to the total thickness of the brazing sheet) in a
range of 5 to 15%.
A brazed assembly according to the present invention comprises a
brazing sheet with a core layer as described above, an interlayer
on one or both sides of the core layer and a clad layer of the
Al--Si-type (filler alloy) on at least one interlayer, that means
on at least one side of the layered structure.
According to another embodiment of the present invention the brazed
assembly comprises a clad layer on both sides of the layered
structure comprising the core layer and two interlayers.
According to another preferred embodiment the assembly of the
present invention has a number of brazing sheets which are
superposing each other so that the interlayer which is
alternatively not covered by a clad layer is facing outwardly and
the superposed brazed sheets are joined together by brazing facing
clad layers.
The present invention also comprises the use of a brazing sheet as
described above or of an assembly as described above for a brazing
application such as a heat exchanger, as for example a radiator, an
oil cooler, an inter cooler, a heater core, an evaporator or a
condenser or similar applications and assemblies which are produced
by joining brazing sheets for forming a compact assembly, mainly
for the purpose of exchanging heat.
The present invention also provides a method for producing an
aluminium alloy brazing sheet having high strength and good
corrosion resistance, comprising the steps of a) casting a core
ingot with the following composition comprising (in weight
percent):
TABLE-US-00006 Zn 1.2 to 5.5 Mg 0.8 to 3.0 Mn 0.1 to 1.0 Cu <0.2
Si <0.35 Fe <0.5, preferably <0.30
optionally one or more selected from the group consisting of:
TABLE-US-00007 Zr <0.3 Cr <0.3 V <0.3 Ti <0.2 Hf
<0.3 Sc <0.5,
the balance aluminium and incidental elements and impurities as a
core material, b) homogenising and/or pre-heating the core ingot
after casting, c) casting a clad ingot comprising an Al--Si based
filler alloy, homogenising and/or pre-heating the clad ingot after
casting and hot rolling said clad ingot to a rolled clad member, d)
superposing the core ingot and the hot rolled clad member to form a
layered member, e) hot rolling the layered member and optionally
cold rolling into a rolled product, f) optionally inter-annealing
between a cold rolling pass or passes, g) optionally end-annealing,
and h) ageing the rolled, preferably by means of natural ageing,
and optionally inter/end-annealed product.
It is furthermore possible to additionally cast an inter ingot
(ingot for producing the interlayer) comprising either an Al--Mn
alloy composition of the AA3xxx-type or pure aluminium of the
AA1xxx-type or an AlMgSi alloy of the AA6xxx-type, each optionally
with the addition of Zn, homogenising and/or pre-heating the inter
ingot after casting and hot rolling the inter ingot to a rolled
inter member (rolled sheet used as an interlayer), and superposing
the core ingot, the inter member and the hot rolled clad member
(rolled sheet used as a clad layer, made from another clad ingot)
to form the layered member. Here, it is advisable to provide a
rectangular groove in the core ingot by scalping out the groove in
the size of the rolled inter member and the hot rolled clad member.
Then, in the groove, a slice of rolled inter member and--on top of
that--a slice of rolled clad member is placed, thereafter using the
edge between the core material and clad material for weld-seaming
the layered structure for hot rolling the layered member and
optionally cold rolling into a rolled product.
According to another preferred embodiment of the invention a new
method for producing a multi-layer brazing sheet is presented: the
method comprises the production of an aluminium alloy multi-clad
brazing sheet by comprising the steps of: a) casting a multiclad
ingot, thereby using a composition as described above as a centre
core layer and an Al--Mn alloy composition of the AA3xxx-type or an
AlMgSi alloy of the AA6xxx-type or pure aluminium of the
AA1xxx-type, optionally with the addition of Zn, as an interlayer
on both sides of the centre core layer, thereby forming the
multiclad ingot (ingot with three layers of material, one centre
core material, covered on both sides with interlayer material), b)
homogenising and/or pre-heating the multiclad ingot after casting,
c) casting a clad ingot comprising an Al--Si based filler alloy,
homogenising and/or pre-heating the clad ingot after casting and
hot rolling the clad ingot to a rolled clad member, and d)
superposing the multiclad ingot and the hot rolled clad member to
form the layered member, e) hot rolling the layered member and
optionally cold rolling into a rolled product, f) optionally
inter-annealing between a cold rolling pass or passes, g)
optionally end-annealing, and h) ageing the rolled, preferably
natural ageing, and optionally inter/end-annealed product.
Such method has the advantage that the core ingot and the
integrated interlayer on both sides of the core ingot are cast at
the same time, thereby reducing the problem of the shifting of
layers during hot rolling/roll cladding.
Other cladding techniques regular in the art such as spray cladding
or continuous cast cladding can be applied in an analogous manner
to produce the multi-layered material of the invention.
The present invention provides also a preferred method for
producing a brazed assembly as described above, by heating an
assembly of brazing sheets, which are superposing each other and
which are produced as described above, preferably through a method
for casting a clad ingot, to the brazing temperature. A typical
brazing cycle comprises for example heating to a first temperature
within a first time interval and to a second temperature within a
second time interval, dwelling said assembly at the second
temperature for a third time interval and cooling the assembly at a
certain cooling rate.
As an example, the first temperature is in a range of about
500.degree. C. to 550.degree. C., the second temperature is in a
range of about 580.degree. C. to 600.degree. C., the first time
interval is in a range of about 8 to 12 minutes, the second time
interval is in a range of about 3 to 7 minutes, the third time
interval is in a range of about 2 to 4 minutes and the cooling rate
is typically in a range of about 50.degree. C./min to 70.degree.
C./min.
Various brazing processes, such as for example vacuum brazing or
controlled atmosphere brazing, the latter with the use of for
example NOCOLOK flux, or fluxless brazing advantageously using
nickel and/or iron and/or cobalt, can be applied.
The present invention hence provides a brazing sheet which showed a
core layer with a very high post-braze strength. The average
post-braze strength (0.2% Proof Strength) was about 165 MPa. The
AA7xxx-type core alloy, in a preferred combination with an
AA3xx3-type interlayer had in the best examples a SWAAT performance
of 47 days without perforations.
The grain structure of the core alloy of the present invention
showed strongly elongated, recrystallized grains, the average grain
size (width.times.length) of about 15.times.250 .mu.m. The alloys
showed a core in which the intermetallics were small, many
intermetallics formed streaks or lines in the rolling direction. An
increased amount of precipitates was formed in the interlayer area
as well as in the core layer. However, in the core layer a few
light streaks with less precipitates were also formed.
In the examples a decreased zinc concentration towards the surface
of the core layer could be found over a depth of about 120 .mu.m.
Hence, the multiclad alloys had a significantly higher corrosion
potential in the surface area caused by the higher concentrations
of zinc in the bulk-core area.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned and other features and advantages of the brazing
sheet according to the invention will become readily apparent from
the following detailed description of some preferred embodiments.
Some examples are shown in the appended drawings:
FIG. 1 shows the basic brazing sheet structure according to the
invention;
FIG. 2 shows a three-layered structure of the brazing sheet of the
invention;
FIG. 3 shows a five-layered structure according to the invention;
and
FIG. 4 shows a section of a light brazed assembly with superposed
brazing sheets of the structure according to FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a basic structure of the brazing sheet according to
the invention with a core layer 1 and a clad layer 2. As shown in
FIG. 2 and FIG. 3 the core layer 1 may be clad on both sides with
the clad layer 2 of the Al--Si based filler alloy type or on one
side with the clad layer 2 and on the other side with an interlayer
3. The other side with the interlayer 3 is exposed to the corrosive
atmosphere.
A preferred embodiment of the invention is shown in FIG. 3 and FIG.
4. The core layer 1 is embedded between two interlayers 3 which are
in turn clad with clad layers 2. By producing an assembly
containing the brazing sheets of the invention, the clad layers 2
accumulate at the corner 4 of two superposed brazing sheets during
brazing thereby being brazed together.
EXAMPLE
On an industrial scale five different aluminium alloys have been
cast into ingots for being used as an Al--Zn core layer for a high
strength aluminium alloy brazing sheet having the following
chemical composition as set out in Table 1.
TABLE-US-00008 TABLE 1 Chemical composition of the DC-cast core
aluminium alloys, in wt. %, Cu 0.02%, Si 0.08%, balance aluminium
and inevitable impurities. Alloying Element Alloy Zn Mg Mn Zr Fe Ti
1 3.50 1.89 0.50 0.145 0.26 0.03 2 4.10 1.64 0.51 0.148 0.27 0.03 3
4.50 1.37 0.49 0.142 0.27 0.03 4 4.50 1.90 0.51 0.139 0.23 0.03 5
4.10 1.69 0.50 0.143 0.25 0.03
The cast ingots were sawn into rolling blocks of about
100.times.80.times.80 mm. These blocks remained unclad. After a
homogenisation these blocks were clad with a brazing filler layer
of an AA4045 alloy and rolled down (to 0.4 mm/1.0 mm) by a process
route comparable to a standard process route used for brazing sheet
materials. The multiclad materials were then end-annealed to an
O-temper condition at 350.degree. C. for 3 h, the heat-up and
cool-down rate was about 30.degree. C./h. The mechanical properties
of the multiclad alloys 1 to 4 in the O-temper condition are given
in Table 2. The post-braze proof strength has been measured after
the multiclad material was subjected to a typical brazing
cycle.
TABLE-US-00009 TABLE 2 Tensile properties and strength of alloys 1
to 4 of Table 1, elongation (formability), incipient melting
temperature (T-Melt) and post-braze proof strength (Rp(p.b.)). Core
Rp Rm A80 Rp (p.b.) T-Melt Alloy (MPa) (MPa) (%) (MPa) (.degree.
C.) 1 109 228 13.0 139 613 2 113 222 10.2 148 618 3 127 215 8.5 135
619 4 114 220 10.4 174 609
Table 2 shows that in O-temper condition the alloys were reasonably
strong. Also the formability of core alloys 1, 2 and 4 was
acceptable (8 13%). The incipient melting point was considerably
above 600.degree. C. Higher amounts of zinc resulted in enhanced
strength properties wherein higher amounts of magnesium also added
strength to the alloy. The preferred target for the post-braze
yield strength (0.2% PS) of 140 MPa could be met with alloys 2 and
4.
Here, it can be seen that the balance of zinc and magnesium is very
important for the strength properties. Furthermore, all core alloys
reached the target incipient melting point wherein silicon and
magnesium are believed to have a much stronger influence on
decreasing the incipient melting point than zinc. The most
promising alloys were alloys No. 2 and 4 showing a very high
strength of 148 MPa and 174 MPa in combination with incipient
melting points of 618.degree. C. and 609.degree. C.
Furthermore, alloy No. 5 has been further tested in combination
with two different interlayer alloys. On an industrial scale two
different aluminium alloys have been cast thereby containing two
different alloy compositions for the interlayer. The chemical
compositions are set out in Table 3.
TABLE-US-00010 TABLE 3 Chemical composition of the DC-cast
interlayer aluminium alloys in weight percent, balance aluminium
and inevitable impurities. Interlayer Alloying Element Alloy Mn Si
Cu Mg Zn Fe 1 1.07 0.19 0.10 0.02 0.00 0.31 2 1.05 0.19 0.10 0.02
1.34 0.31
Both alloys as shown in Table 3 were used in combination with a
core layer comprising alloy No. 5 of Table 1. The post-braze
mechanical properties of the various clad materials after 35 days
of natural ageing have been tested and are listed in Table 4.
The incipient melting points measured by DSC, for two multiclad
materials are given in Table 5. The incipient melting point has
been measured on pre-brazed plate materials, in end-annealed,
O-temper condition.
TABLE-US-00011 TABLE 4 Post-braze mechanical properties after 35
days of natural ageing, corrosion performance (SWAAT test according
to ASTM G85) of the multiclad materials,in combination with various
thicknesses, end of test after 50 days. Alloy Rp Rm A80 SWAAT
Thickness Core/Inter MPa MPa % days mm 5 1 164 291 13.2 14 0.4 5 2
159 284 14.3 5 0.4 5 1 168 306 17.0 47 1.0 5 2 168 304 17.5 42
1.0
TABLE-US-00012 TABLE 5 Incipient melting points measured by DSC.
Alloy Incipient Core Interlayer T (.degree. C.) 5 1 615 5 2 613
The incipient melting points of the combination of core alloy No. 5
and interlayer alloys 1 or 2 are more than sufficient. The SWAAT
test results show excellent corrosion behaviour of the materials
when compared to standard brazing materials. Furthermore, it has
been shown that the corrosion resistance of an interlayer without
zinc is better than of an interlayer comprising zinc as identified
above. It appears recommendable to either use a thickness of more
than 0.5 mm and/or to use interlayer alloy 1 in order to obtain the
better corrosion performance. Hence, the multiclad or multilayered
brazing sheet of the invention has a very high post braze strength
in combination with very good corrosion properties and a relatively
high incipient melting point thereby adding good brazing properties
to the structure. Specifically, the post-braze strength properties
of alloy No. 4 of 174 MPa is superior to most of the prior art core
alloys. Hence, the multiclad layered brazing sheet of the invention
has a very high post-braze strength in combination with very good
corrosion properties and a relatively high incipient melting point
thereby adding good brazing properties to the structure.
Having now fully described the invention, it will be apparent to
one of ordinary skill in the art that many changes and
modifications can be made without departing from the spirit and
scope of the invention as hereon described.
* * * * *